Welding is ubiquitous in modern manufacturing. Perhaps one of the most popular welding processes for joining metallic materials is arc welding. For instance, gas metal arc welding (“GMAW”) normally utilizes a direct current electrode positive polarity in which a wire is connected to the positive terminal of the power source and the power source operates in a constant voltage (“CV”) mode. This results in a reverse polarity that contributes to a stable arc, uniform metal transfer, and greater weld penetration. The CV power source can be adjusted to vary the welding current such that the wire melting speed is equal to the given wire feed, speed, so that the welding voltage or arc length is maintained constant.
Many automotive manufacturing facilities utilize automatic or semiautomatic GMAW of metallic automobile components. The productivity for such GMAW is generally determined by the travel speed of the welder/base metal that creates the desired weld profile. Currently, a faster travel speed requires a larger welding wire melting speed, so that there is enough melted metal to form a longer weld bead in a unit time. The melting speed can generally be calculated from the following formula (assuming the metal transfer is in spray mode, i.e., die melting current is greater than 250 amps for mild steels):
      m    .    =            5.1      ×              10                  -          13                    ⁢                                    I            2                    ⁢          L                S              +          2.2      ×              10                  -          6                    ⁢      I      Where {dot over (m)} (kg/s) is the melting speed, I(A) is the total melting current, L(m) is the wire extension, and S(m2) is the cross-sectional area of the wire. From this formula, it can be seen that the current must be increased in order to increase the melting speed.
Unfortunately, given the current configuration of conventional GMAW, the melting current is the same as the base metal current. Therefore, an increase in the melting current results in an increase in the base metal heat input. In other words, to melt the weld wire faster, one must increase the melting current and the base metal heat input. This increase in base metal heat input results in increased residual stress and distortion in the base metal being welded. For this reason, it is difficult to increase the welding speed for the GMAW process without imposing undesired amounts of heat to the base metal.
While use of tandem, independent GMAW configurations and variable-polarity GMAW systems have had limited success in increasing the melting speed of the welding wire, they are expensive and limited in their weld control. The tandem and variable-polarity systems do not allow for independent control of the base metal heat input, while simultaneously allowing the user to control the melting speed of the weld wire. Also, these systems often require manufacturers to completely replace the welding systems they currently have in place. That is, the conventional GMAW system that a manufacturer would have in place must be replaced with a newly configured tandem or variable-polarity system.
Accordingly, the need exists for an arc welder and related system and method that allow for greater control of the welding process. The welder would enable greater melting speeds of the welding wire, while allowing control of certain aspects of the base metal being welded. The welder, system, and method would also be capable of being used with conventional GMAW systems, thus obviating the need to completely replace existing welding systems.